Mechanism Research Of Coalescence-induced Droplet Jumping Amoung Two-phase Fluids On Hydrophobic Fibers

Coalescence-induced droplet jumping can quickly remove droplets from fibers and enhance the self-cleaning property of hydrophobic fibers.To elucidate the mechanism and the factors of influencing the coalescence-induced droplet jumping on hydrophobic fibers,the behaviors of two droplets coalescing and jumping on hydrophobic fibers were investigated theoretically and experimentally in this dissertation.In the theoretical research,a novel model for coalescence of two droplets on hydrophobic fibers was firstly developed based on the energy balance,where the effects of droplet radius,fiber radius,fiber curvature,and the surface roughness and wettability of fiber were totally considered.The dynamics of two droplets coalescence and induced jumping on hydrophobic fibers was researched for understanding the effects of droplet and fiber radii on all energy terms and jumping velocity of merged droplet.Meanwhile the effects of the Ohnesorge number,the relative radius of droplet and fiber as well as the surface wettability of fiber on the dimensionless jumping velocity of merged droplet on hydrophobic fiber were investigated too based on a scaling law.In the experimental research,the coalescence-induced droplet jumping on hydrophobic fibers in a stationary viscous fluid and the process of water droplets coalescing on the hydrophobic fibers of 304 stainless steel fibers in a flowing water/oil emulsion were studied by using high speed camera.For two droplets coalescence on a hydrophobic fiber in a stationary viscous fluid,the effects of bulk fluid on the coalescence-induced droplet jumping were investigated with various liquids separatedly,including n-hexane,n-dodecane and toluene.Besides,the dynamic characteristics of merged droplets on hydrophobic fibers were used to evaluate the effects of buld fluid viscosity and water-oil interfacial tension on the coalescenceinduced droplet jumping on hydrophobic fiber.In a flowing water/oil emulsion,the coalescence process of water droplets on hydrophobic fibers were studied under different operating conditions: feed speeds of 0.6 ～ 2.1m L/min;fiber radius of 8 μm,52 μm,152 μm;oil viscosity of 4.65 m Pa.s,7.63 m Pa.s and 99.6 m Pa.s.The speed of water droplet colliding fiber and the number and radius of water droplets adhering on fibers were used to evaluate the effects of operating conditions on the process of water coalescence on hydrophobic fibers.The results of this thesis provide the theoretical foundations for the control of coalescence-induced droplet jumping on hydrophobic fiber,and provide technical guidance for the industrial applications utilizing the coalescence-induced droplet jumping to enhance the self-cleaning properties of hydrophobic fibers.There is important theoretical significance and application value for solving the problems of high pressure and low filtration efficiency caused by effusion during the usage of fiberbased filtration equipment.